Chapter II: Operations on Land (3)

Down to the middle of the 19th century natural dyestuffs alone, with but few exceptions, were at the command of the dyer. But already in the year 1834 the German chemist Runge noticed that one of the products obtained by distilling coal-tar, namely, aniline, gave a bright blue coloration under the influence of bleaching powder. No useful colouring matter, however, was obtained from this product, and it was reserved for the English chemist Sir W.H. Perkin to prepare the first aniline dye, namely, the purple colouring matter Mauve (1856). The discovery of other brilliant aniline dyestuffs followed in rapid succession, and the dyer was in the course of a few years furnished with Magenta, Aniline Blue, Hofmann's Violet, Iodine Green, Bismarck Brown, Aniline Black, &c. Investigation has shown that the products of the distillation of coal-tar are very numerous, and some of them are found to be specially suitable for the preparation of colouring matters. Such, for example, are benzene, naphthalene and anthracene, from each of which distinct series of colouring matters are derived. In 1869 the German chemists Graebe and Liebermann succeeded in preparing Alizarin, the colouring matter of the madder-root, from the coal-tar product anthracene, a discovery which is of the greatest historical interest, since it is the first instance of the artificial production of a vegetable dyestuff. Another notable discovery is that of artificial Indigo by Baeyer in 1878. Since 1856, indeed, an ever-increasing number of chemists has been busily engaged in pursuing scientific investigations with the view of preparing new colouring matters from coal-tar products, and of these a few typical colours, with the dates of their discovery, may be mentioned: Cachou de Laval (1873); Eosin (1874); Alizarin Blue (1877); Xylidine Scarlet (1878); Biebrich Scarlet (1879); Congo Red (1884); Primuline Red (1887); Rhodamine (1887); Paranitraniline Red (1889); Alizarin Bordeaux (1890); Alizarin Green (1895). At the present time it may truly be said that the dyer is furnished with quite an embarrassing number of coal-tar dyestuffs which are capable of producing every variety of colour possessing the most diverse properties. Many of the colours produced are fugitive, but a considerable number are permanent and withstand various influences, so that the general result for some years has been the gradual displacement of the older natural dyestuffs by the newer coal-tar colours.

During this period of discovery on the part of the chemist, the mechanical engineer has been actively engaged in devising machines suitable for carrying out, with a minimum of manual labour, all the various operations connected with dyeing. This introduction of improved machinery into the dyeing trade has resulted in the production of better work, it has effected considerable economy, and may be regarded as an important feature in modern dyeing.

General principles.

The art of dyeing is a branch of applied chemistry in which the dyer is continually making use of chemical and physical principles in order to bring about a permanent union between the material to be dyed and the colouring matter applied. If cotton or wool is boiled in water containing finely powdered charcoal, or other insoluble coloured powder, the material is not dyed, but merely soiled or stained. This staining is entirely due to the entanglement of the coloured powder by the rough surface of the fibre, and a vigorous washing and rubbing suffices to remove all but mere traces of the colour. True dyeing can only result when the colouring matter is presented to the fibre in a soluble condition, and is then, by some means or other, rendered insoluble while it is absorbed by, or is in direct contact with, the fibre. There must always be some marked physical or chemical affinity existing between fibre and colouring matter, and this depends upon the physical and chemical properties of both. It is well known that the typical fibres, wool, silk and cotton, behave very differently towards the solution of any given colouring matter, and that the method of dyeing employed varies with each fibre. As a general rule wool has the greatest attraction for colouring matters, and dyes most readily; cotton has the least attraction, while silk occupies in this respect an intermediate position. These differences may be to some extent due to differences of physical structure in the fibres, but they are mainly due to their different chemical composition.

On the other hand, a given fibre, e.g. cotton, behaves quite differently in dyeing towards various colouring matters. Some of these are not at all attracted by it, and are incapable of being used as dyestuffs for cotton. For others cotton exhibits a marked attraction, so that it is readily dyed by mere steeping in a hot solution of the colouring matter. Again, for other colouring matters cotton has little or no attraction, and cannot be dyed with them until it has been previously impregnated or prepared with a metallic salt, tannic acid or some other agent which is capable of combining with the colouring matter and precipitating it as an insoluble coloured compound within or upon the fibre. Such differences of behaviour are to be ascribed to differences in the chemical constitution or atomic arrangement of the various colouring matters.

Classification of colouring matters.

In the case of the coal-tar colours we are, for the most part, well acquainted with their chemical constitution, and in accordance with this knowledge the chemist has arranged them in the following groups:--(1) Nitro Colours. (2) Azo Colours, including Amido-azo, Oxy-azo, Tetrazo and Polyazo Colours. (3) Hydrazone Colours. (4) Oxy-quinone Colours, including Quinone-oxime Colours. (5) Diphenylmethane and Triphenylmethane Colours, including Rosaniline, Rosolic acid and Phthaleine Colours. (6) Quinoneimide Colours, including Indamine, Indophenol, Thiazime, Thiazone, Oxazime, Oxazone, Azine, Induline, Quinoxaline and Fluorindine Colours. (7) Aniline Black. (8) Quinoline and Acridine Colours. (9) Thiazol Colours. (10) Oxy-ketone, Xanthone, Flavone and Cumarine Colours. (11) Indigo. (12) Colours of unknown constitution.

This arrangement of the colouring matters in natural chemical groups is well suited for the requirements of the chemist, but another classification is that based on the mode of their application in dyeing. This is much simpler than the previous one, and being better adapted for the practical purposes of the dyer, as well as for explaining the various methods of dyeing, it is preferred for this article. According to this arrangement colouring matters are classified under the following groups:--(1) _Acid Colours._ (2) _Basic Colours._ (3) _Direct Colours._ (4) _Developed Colours._ (5) _Mordant Colours._ (6) _Miscellaneous Colours._ (7) _Mineral Colours._ It is well to state that there is no sharp line of division between some of these groups, for many colours are applicable by more than one method, and might quite well be placed in two, or even three, of the above groups. This may be due either to the kind of fibre to which the colouring matter is to be applied, or to certain details in the chemical constitution of the latter which give it a twofold character.

ACID COLOURS.--These dyestuffs are so called because they dye the
animal fibres wool and silk in an acid bath; they do not dye cotton.
From a chemical point of view the colouring matters themselves are of
an acid character, this being due to the presence in the molecule of
nitro (NO2) or sulphonic acid (HSO3) groups. According to their origin
and constitution they may be distinguished as nitro compounds,
sulphonated azo compounds and sulphonated basic colours. The acid
colours are usually sold in the form of their alkali salts, as
variously coloured powders soluble in water. For the alkali salts in
neutral or alkaline solution wool and silk have little or no affinity,
but dyeing rapidly occurs if the solution is acidified with sulphuric
acid whereby the colour-acid is liberated. This addition of acid,
however, is necessary not only to set free the colour-acid of the
dyestuff, but also to alter partially the chemical composition of the
fibre, and thus render it capable of uniting more readily with the
free colour-acid. It has been shown, namely, that if wool is boiled
with dilute sulphuric acid, and then thoroughly washed with
boiling-water till free from acid, it acquires the property of being
dyed with acid colours even in neutral solution. By this treatment a
portion of the wool substance is converted into so-called _lanuginic
acid_, which has a strong attraction for the colour-acid of the
dyestuff, with which it forms an insoluble coloured compound. For
dyeing _wool_, the general rule is to charge the dyebath with the
amount of dyestuff necessary to give the required colour, say from 1/2
to 2 or 6 % on the weight of wool employed, along with 10% sodium
sulphate (Glauber's salt) and 4% sulphuric acid (1.84 sp. gr.). The
woollen material is then introduced and continually handled or moved
about in the solution, while the temperature of the latter is
gradually raised to the boiling point in the course of 3/4 to 1 hour;
after boiling for 1/4 to 1/2 hour longer, the operation is complete,
and the material is washed and dried.

In practice, modifications of this normal process may be introduced,
in order to ensure the dyeing of an even colour, i.e. free from such
irregularities as cloudiness, streaks, &c., which may be due to the
quality of the material or to the special properties of the acid
colour employed. Materials of a firm, close texture, also the
existence of a strong affinity between fibre and colouring matter, do
not generally lend themselves to the dyeing of even colours, or to a
satisfactory penetration of the material. Some acid colours dye even
colours without any difficulty; others, however, do not. The addition
of sodium sulphate to the dyebath exerts a restraining action; the
dyeing therefore proceeds more slowly and regularly, and a more equal
distribution and better absorption of the colouring matter takes
place. Other devices to obtain even colours are: the use of old
dye-liquors, a diminished amount of acid, the employment of weaker
acids, e.g. acetic or formic acid or ammonium acetate, and the
entering of the material at a low temperature.

In the application of so-called Alkali Blue the process of dyeing in
an acid bath is impossible, owing to the insolubility of the
colour-acid in an acid solution. Wool and silk, however, possess an
affinity for the alkali salt of the colouring matter in neutral or
alkaline solution, hence these fibres are dyed with the addition of
about 5% borax; the material acquires only a pale colour, that of the
alkali salt, in this dyebath, but by passing the washed material into
a cold or tepid dilute solution of sulphuric acid a full bright blue
colour is developed, due to the liberation of the colour-acid within
the fibre. In the case of other acid colours, e.g. Chromotrope, Chrome
Brown, Chromogen, Alizarin Yellow, &c., the dyeing in an acid bath is
followed by a treatment with a boiling solution of bichromate of
potash, alum, or chromium fluoride, whereby the colouring matter on
the fibre is changed into insoluble oxidation products or
colour-lakes. This operation of developing or fixing the colour is
effected either in the same bath at the end of the dyeing operation,
or in a separate bath. See also ARTIFICIAL MORDANT COLOURS.

When dyeing with certain acid colours, e.g. Eosine, Phloxine and other
allied bright pink colouring matters derived from resorcin, the use of
sulphuric acid as an assistant must be avoided, since the colours
would thereby be rendered paler and duller, and only acetic acid must
be employed.

The properties of the dyes obtained with the acid colours are
extremely varied. Many are fugitive to light; on the other hand, many
are satisfactorily fast, some even being very fast in this respect. As
a rule, they do not withstand the operations of milling and scouring
very well, hence acid colours are generally unsuitable for tweed yarns
or for loose wool. They are largely employed, however, in dyeing other
varieties of woollen yarn, silk yarn, union fabrics, dress materials,
leather, &c. Previous to the discovery of the coal-tar colours very
few acid colours were known, the most important one being Indigo
Extract. Prussian Blue as applied to wool may also be regarded as
belonging to this class, also the purple dyestuff known as Orchil or
Cudbear.

The following list includes some of the more important acid colours
now in use, arranged according to the colour they yield in dyeing:--

_Red._--Wool scarlet, brilliant scarlet, erythrine, crocein scarlet,
brilliant crocein, violamine G, scarlet 3R, crystal scarlet, new
coccine, chromotrope 2R, azo acid magenta, Victoria scarlet, xylidine
scarlet, Palatine scarlet, Biebrich scarlet, pyrotine, orchil red,
Bordeaux B, milling red, azo carmine, acid magenta, fast acid violet A
2R, naphthylamine red, fast red, claret red, eosine, erythrosine, rose
Bengale, phloxine, cyanosine, cloth red, lanafuchsine, rosinduline,
erio carmine.

_Orange._--Diphenylamine orange, methyl orange, naphthol orange,
crocein orange, brilliant orange, orange G, orange N, mandarin G R.

_Yellow._--Picric acid, naphthol yellow S, fast yellow, brilliant
yellow S, azoflavine, metanil yellow, resorcine yellow, tartrazine,
quinoline yellow, milling yellow, azo yellow, Victoria yellow,
brilliant yellow S, citronine, Indian yellow.

_Green._--Acid green, guinea green, fast green, patent green, cyanol
green, erio green, brilliant acid green 6 G.

_Blue._--Alkali blue, soluble blue, opal blue, methyl blue, Hochst new
blue, patent blue, ketone blue, cyanine, thiocarmine, fast blue,
induline, violamine 3 B, azo acid blue, wool blue, indigo extract,
erio glaucine, erio cyanine, erio blue, lanacyl blue, sulphon-azurine,
sulphon-cyanine.

_Violet._--Acid violet, red violet, regina violet, formyl violet,
violamine B, fast violet, azo acid violet, erio violet, lanacyl
violet.

_Brown._--Fast brown, naphthylamine brown, acid brown, resorcine
brown, azo brown, chrome brown, chromogene.

_Black._--Naphthol black, azo black, wool black, naphthylamine black,
jet black, anthracite black, Victoria black, azo acid black, brilliant
black, union black, brilliant black B.

BASIC COLOURS.--These colouring matters are the salts of organic
colour-bases, their name being derived from the fact that their dyeing
power resides entirely in the basic part of the salt. In the free
state the bases are colourless and insoluble, but in combination with
acids they form salts which are coloured and for the most part soluble
in water. They are usually sold in the form of powder or crystals, the
latter exhibiting frequently a beautiful metallic lustre. _Wool_ and
_silk_ are dyed in a neutral bath, i.e. without any addition, the
material not requiring any previous preparation. During the dyeing
operation the animal fibres appear to play the part of an acid, for
they decompose the colouring matter and unite with the colour-base to
form an insoluble coloured salt or lake, while the acid of the
colouring matter is liberated and remains in solution. Although, as a
rule, a neutral dyebath is employed in dyeing wool, a slight addition
(2%) of soap is sometimes made in order to give a brighter colour,
while in other cases, e.g. with Victoria Blue, the dyebath must of
necessity be made distinctly acid with acetic or sulphuric acid. Silk
is usually dyed in a bath containing "boiled-off liquor" (i.e. the
spent soap-liquor from the operation of scouring) neutralized or
slightly acidified with acetic or tartaric acid. For a full colour use
2 or 3% colouring matter, enter the wool at a low temperature, heat
gradually to near the boiling point in the course of 3/4 hour, and
continue dyeing for 1/4 hour. Owing to the slight solubility of many
basic colours, it is important to take the precaution of filtering the
colour solution into the dyebath through a flannel filter, also to
neutralize the alkalinity of calcareous water with a little acetic
acid, to prevent decomposition of the colouring matter and
precipitation of the colour-base.

Unlike the animal fibres, _cotton_ has little or no affinity for the
basic colours; hence the cotton dyer makes use of the fact that cotton
has a natural attraction for tannic acid, and that the latter forms
insoluble lakes with the bases of basic colours. Previous to dyeing,
the cotton is prepared with tannic acid by steeping in a cold solution
of the latter for several hours; cotton pieces are run at full width
through a solution containing 2 to 6 oz. per gallon of tannic acid,
and after being evenly squeezed are dried on steam cylinders. The
cotton is then worked in a solution of tartar emetic or stannic
chloride, so that the tannic acid absorbed by the fibre may be fixed
upon it as insoluble tannate of antimony or tin. Although the tannic
acid is thus united with metallic oxide, it still has the power of
attracting the base of the colouring matter, and there is fixed upon
the fibre an insoluble colour-lake, namely, a tannate of antimony and
colour-base, which constitutes the dye. In this process the tannic
acid is called the _mordant_, the tartar emetic acts as the
_fixing-agent_ for the tannic acid, and the cotton as finally prepared
for dyeing is said to be _mordanted_. The proportions employed,
reckoned on the weight of cotton, may vary from 2 to 10% tannic acid,
or the equivalent in a decoction of sumach, myrabolans, or other
tannin matter, and 1/2 to 3% tartar emetic. After mordanting and
fixing of the mordant, the cotton is well washed and dyed in the cold
or at 60 deg. C. for 1/2 to 1 hour with the necessary colouring
matter. Applied in this manner, basic colours are moderately fast to
soap, but generally not to the action of light.

_Linen_ is dyed in the same manner as cotton. Jute is dyed without any
previous preparation, since it behaves like a tannin-mordanted fibre,
attracting the basic colours direct.

The basic colours, to which class most of the earlier coal-tar colours
belonged, are remarkable for their great colouring power, and in most
cases for the brilliancy of the colours they yield. With the exception
of certain dark colours, they are fugitive to light. It is interesting
to note that only one vegetable colouring matter is at present
recognized as belonging to this class, namely, the yellow dyestuff
barberry bark and root (_Berberis vulgaris_) which contains the
alkaloid berberine.

The following is a list of the more important basic colours derived
from coal-tar:--

_Red._--Magenta, safranine, rhodamine, pyronine red, rhoduline red,
rosazein, induline scarlet.

_Orange._--Chrysoidine, phosphine, acridine orange, tannin orange.

_Yellow._--Auramine, benzoflavine, thioflavine T, acridine yellow,
homophosphine, rhoduline yellow.

_Green._--Malachite green, emerald green, imperial green, China green,
brilliant green, Victoria green, diamond green, methylene green, azine
green.

_Blue._--Methylene blue, new methylene blue, toluidine blue, thionine
blue, indamine blue, Victoria blue, night blue, Nile blue, turquoise
blue, marine blue, indoine blue, metamine blue, Capri blue, indazine,
metaphenylene blue, paraphenylene blue, toluylene blue, indigene,
indol blue, diphene blue, setopaline, setocyanine, setoglaucine,
Helvetia blue.

_Violet._--Methyl violet, crystal violet, ethyl purple, methylene
violet, mauve, paraphenylene violet, rhoduline violet, methylene
heliotrope.

_Brown._--Bismarck brown.

_Black._--Diazine black.

_Grey._--Methylene grey, nigrisine, new grey.

DIRECT COLOURS.--The characteristic feature of the dyestuffs belonging
to this class is that they dye cotton "direct"--i.e. without the aid
of mordants. Two distinct series of colouring matters of this group
may be distinguished--namely, _Direct Cotton Colours_ and _Sulphide
Colours_.

(a) _Direct Cotton Colours._--The colours of this class are frequently
called the Substantive Cotton Colours, Benzo Colours, Diamine Colours,
Congo Colours. Considered from the chemical point of view, they are
mostly alkali salts of sulphonated tetrazo colours obtained by
diazotizing certain diamido compounds, e.g. benzidine,
diamido-stilbene, &c., and uniting the products thus obtained with
various amines or phenols. The first colouring matter of this class
was the so-called Congo red, discovered in 1884, and since that time a
very great number have been introduced which yield almost every
variety of colour. The method of dyeing _cotton_ consists in merely
boiling the material in a solution of the dyestuff, when the cotton
absorbs and retains the colouring matter by reason of a special
natural affinity. The concentration of the dyebath is of the greatest
importance, since the amount of colour taken up by the fibre is in an
inverse ratio to the amount of dye liquor present in the bath. The
addition of 1 to 3 oz. sodium sulphate and 1/12 to 1/3 oz. carbonate
of soda per gallon gives deeper colours, since it diminishes the
solubility of the colouring matter in the water and increases the
affinity of the cotton for the colouring matter. An excess of sodium
sulphate is to be avoided, otherwise precipitation of the colouring
matter and imperfect dyeing result. With many dyestuffs it is
preferable to use 1/6 to 1/3 oz. soap instead of soda. On cotton the
dyed colours are usually not very fast to light, and some are
sensitive to alkali or to acid, but their most serious defect is that
they are not fast to washing, the colour tending to run and stain
neighbouring fibres. Their fastness to light and washing is, however,
greatly improved by a short (1/2 hour) after-treatment with a boiling
solution of copper sulphate (3%), with or without the addition of
bichromate of potash (1%). _Wool_ and _silk_ are dyed with the direct
colours either neutral or with the addition of a little acetic acid to
the dyebath. On these fibres the dyed colours are usually faster than
on cotton to washing, milling and light; some are very fast even to
light--e.g. Diamine fast red, chrysophenine, Hessian yellow, &c. Many
of the Direct Colours are very useful for dyeing plain shades on union
fabrics composed of wool and cotton, silk and cotton, or wool and
silk. Owing to the facility of their application, they are also very
suitable for use as household dyes, especially for cotton goods.

A few vegetable dyestuffs belong to this class, notably Turmeric,
saffron, annatto and safflower, but they all yield colours which are
fugitive to light, and they are now of little importance. _Turmeric_
is the underground stem or tuber of _Curcuma tinctoria_, a plant
growing abundantly in the East Indies. It dyes cotton, wool and silk
in a bath acidified with acetic acid or alum, yielding a bright yellow
colour which is turned brown by alkalis. _Saffron_ consists of the
stigmata of the flower of _Crocus sativus_, which is grown in Austria,
France and Spain. It dyes a bright orange-yellow colour. _Annatto_ is
the pulpy mass surrounding the seeds of _Bixa orellana_, a plant which
grows in South America--e.g. Brazil, Cayenne, &c. It dyes cotton and
silk in an alkaline or soap bath an orange colour, which is turned red
by acids. _Safflower_ consists of the dried florets of _Carthamus
tinctorius_, which is grown in the East Indies, Egypt and southern
Europe. Cotton is dyed a brilliant pink colour by working it in a cold
alkaline (sodium carbonate) extract of the colouring matter, while
gradually acidifying the solution with citric acid (lime-juice).

The Direct Colours which are derived from coal-tar products are very
numerous indeed; they are largely employed, and occupy a very
important position among dyestuffs. The following list includes the
principal coal-tar colours of this group:--

_Red._--Congo red, brilliant Congo, benzopurpurine, brilliant
purpurine, deltapurpurine, diamine scarlet, diamine fast red,
rosazurine, salmon red, erica, Titan pink, St Denis red, Columbia red,
naphthylene red, Congo rubine, acetopurpurine, dianol red, thiamine
crimson, geranine, brilliant geranine, Columbia fast scarlet, benzo
fast scarlet, thiamine red, diamine rose, Dongola red, rosophenine.

_Orange._--Congo orange, benzo orange, toluylene orange, mikado
orange, brilliant orange, Columbia orange, diamine orange, pyramine
orange, benzo fast orange.

_Yellow._--Chrysamine, cresotin yellow, diamine yellow, carbazol
yellow, chrysophenine, Hessian yellow, curcumine yellow, thiazol
yellow, thioflavine S, oriol, mimosa yellow, Columbia yellow, cotton
yellow, chloramine yellow, direct yellow, diamine fast yellow, diamine
gold, sun yellow, stilbene yellow, chlorophenine, oxyphenine.

_Green._--Benzo olive, Columbia green, benzo green, diamine green,
direct green, diphenyl green, oxamine green, eboli green.

_Blue._--Azo blue, benzoazurine, brilliant azurine, sulphon-azurine,
diamine blue, benzo indigo blue, benzo black blue, Chicago blue,
Columbia blue, Erie blue, Zambezi blue, benzo cyanine, Congo blue,
diamine sky blue, brilliant benzo blue, benzo chrome black blue,
oxamine blue, diphenyl blue, diamineral blue, diaminogene, benzo fast
blue, diazo indigo blue, brilliant chlorazol blue.

_Violet._--Hessian purple, Congo Corinth, heliotrope, Congo violet,
diamine violet, Hessian violet, azo violet, benzo violet, violet
black, diamine Bordeaux, chlorantine lilac, diphenyl violet, triazol
violet, Columbia violet.

_Brown._--Benzo brown, Congo brown, toluylene brown, diamine brown,
cotton brown, Hessian brown, terra-cotta, mikado brown, catechu brown,
wool brown, Columbia brown, Zambezi brown, benzo chrome brown, direct
fast brown, direct bronze brown, chloramine brown, triazol brown,
toluylene brown, dianol brown, Crumpsall direct fast brown.

_Black._--Diamine black, Columbia black, Nyanza black, Tabora black,
Zambezi black, chromanil black, benzo black, benzo fast black, direct
blue black, Pluto black, oxydiamine black, diamine jet black,
polyphenyl black, union black, triazol black, Titan black, cotton
black, oxamine black.

_Grey._--Benzo grey, benzo black, azo mauve, diaminogene, neutral
grey.

(b) _Sulphide Colours._--These dyestuffs are only suitable for dyeing
the vegetable fibres, since they must be applied in a strongly
alkaline bath. The dyestuff Cachou de Laval, discovered in 1873, was
the first member of this group, and was obtained by melting a mixture
of sodium sulphide and various organic substances--e.g. bran, sawdust,
&c. In recent years numerous other dyestuffs have been added to the
list, namely, grey, blue, green, brown, and especially black colours,
by submitting certain definite amido compounds of the aromatic series
to a similar treatment with sodium sulphide or sodium thiosulphate,
and subsequent oxidation. The mode of dyeing with these colours is
based on the fact that they are soluble in an alkaline reducing agent,
and if the cotton is worked in the solution, subsequent oxidation
develops the colour, which is fixed upon the fibre in an insoluble
condition. The material is boiled for about one hour in a solution of
the colour (10 to 15%), with the addition of sodium carbonate (1 to
10%), common salt (10 to 20%), and sodium sulphide (5 to 30%); it is
then washed in water, and may be developed by heating in a bath
containing 2 to 5% of bichromate of soda, and 3 to 6% acetic acid. A
final washing with water containing a little soda to remove acidity is
advisable. The sulphide colours are remarkable for their fastness to
light, alkalis, acids and washing, but unless proper care is exercised
the cotton is apt to be tendered on being stored for some time.

The following list includes some of the most important of the colours
of this class:--

_Yellow._--Immedial yellow, pyrogene yellow, sulphur yellow, thion
yellow, thiogene yellow.

_Orange._--Eclipse phosphine, immedial orange, pyrogene orange, thion
orange, thiogene orange.

_Green._--Pyrogene green, Italian green, eclipse green, pyrol green,
immedial green, katigene green, thionol green.

_Blue._--Immedial blue, immedial sky blue, eclipse blue, katigene
indigo, pyrogene blue, sulphur blue, thion blue, thiogene blue.

_Violet._--Katigene violet, thiogene heliotrope, thiogene purple.

_Brown._--Pyrogene brown, pyrogene yellow, Cachou de Laval,
thiocatechine, katigene black brown, eclipse brown, immedial brown,
katigene brown, dianol brown.

_Grey and Black._--Pyrogene grey, Vidal black, immedial black,
katigene black, anthraquinone black, St Denis black, amidazol black,
cross dye black, eclipse black, carbide black, thiogene black,
sulphaniline black, sulfogene black, pyrogene black, dianol black,
sulphur black, thion black, kryogene black.

This class of colours is continually increasing in number, and for
certain purposes in cotton dyeing the group has acquired great
importance.

DEVELOPED COLOURS.--This group includes certain azo colours which are
developed or produced upon the fibre itself (usually _cotton_) by the
successive application of their constituent elements. It may be
conveniently divided into the following sub-groups:--Insoluble Azo
Colours, Developed Direct Colours, Benzo Nitrol Colours.

(a) The _Insoluble Azo Colours_ are produced as insoluble coloured
precipitates by adding a solution of a diazo compound to an alkaline
solution of a phenol, or to an acid solution of an amido compound. The
necessary diazo compound is prepared by allowing a solution containing
nitrous acid to act upon a solution of a primary aromatic amine. It is
usually desirable to keep the solutions cool with ice, owing to the
very unstable nature of the diazo compounds produced. The colour
obtained varies according to the particular diazo compound, as well as
the amine or phenol employed, [beta]-naphthol being the most useful
among the latter. The same coloured precipitates are produced upon the
_cotton_ fibre if the material is first impregnated with an alkaline
solution of the phenol, then dried and passed into a cold solution of
the diazo solution. The most important of these colours is
_para-nitraniline red_, which is dyed in enormous quantities on cotton
pieces. The pieces are first "prepared" by running them on a padding
machine through a solution made up of 30 grms. [beta]-naphthol, 20
grms, caustic soda, 50 grms. Turkey red oil, and 5 grms. tartar emetic
in 1000 grms. (1 litre) water. They are then dried on the
drying-machine, and are passed, after being allowed to cool, into the
diazo solution, which is prepared as follows: 15 grms. para-nitraniline
are dissolved in 53 c.c. hydrochloric acid (34 deg. Tw.) and a
sufficiency of water. To the cold solution a solution of 10-1/2 grms.
sodium nitrite is added while stirring. The whole is then made up to
1200 c.c., and just before use 60 grms. sodium acetate are added. The
colour is developed almost immediately, but it is well to allow the
cotton to remain in contact with the solution for a few minutes. The
dyed cotton is squeezed, washed, soaped slightly, and finally rinsed in
water and dried. A brilliant red is then obtained which is fast to soap
but not to light. If the para-nitraniline used in the foregoing process
is replaced by meta-nitraniline, a yellowish-orange colour is obtained;
with [alpha]-naphthylamine, a claret-red; with amido-azo-toluene, a
brownish red; with benzidine, a dark chocolate; with dianisidine, a
dark blue; and so on. The dyed colours are fast to washing and are much
used in practice, particularly the para-nitraniline red, which serves
as a substitute for Turkey-red, although it is not so fast to light as
the latter.

(b) _Developed Direct Colours._--The primuline colours were the first
representatives of this class and are derived from the yellow dyestuff
known as primuline, which dyes cotton in the same manner as the direct
colours. The primuline yellow thus obtained is fugitive to light and
of little practical value, but since the colouring matter is an amido
base it can be diazotized in the fibre and then developed in solutions
of phenols or amines, whereby azo dyes of various hues may be
obtained, according to the developer employed; thus, [beta]-naphthol
develops a bright red colour, resorcin develops an orange, phenol a
yellow, naphthylamine a brown, &c. The _dyeing_ of the primuline
yellow is effected by boiling the cotton for one hour in a solution of
primuline (5%) and common salt (10 to 20%). The diazotizing operation
consists in passing the dyed and rinsed cotton for 5 to 10 minutes
into a cold solution of nitrous acid--i.e. a solution of 3/4 oz.
sodium nitrite per gallon of water, slightly acidified with sulphuric
acid. The diazotized material should not be exposed to light, but at
once washed in cold water and passed into the developer. The
_developing_ process consists in working the diazotized material for 5
to 10 minutes in a cold solution of the necessary phenol, and finally
washing with water. The only developer of any practical importance is
a solution of [beta]-naphthol in caustic soda, which produces
primuline red. The primuline colours are best adapted for _cotton_
dyeing, and the colours obtained are fast to washing and to moderate
soaping, but they are not very fast to light.

If _cotton_ is dyed with other direct colours containing free amido
groups, the colour can be diazotized on the dyed fibre exactly in the
same manner as in the case of primuline-dyed cotton, and then
developed by passing into the solution of an amine or phenol, or by
treating it with a warm solution of sodium carbonate. In this manner a
new azo dye is produced upon the fibre, which differs from the
original one not only in colour, but also by being faster to washing
and other influences. A treatment with copper sulphate solution after
development is frequently beneficial in rendering the colour faster to
light. Some Direct Colours, indeed, are of little value, owing, for
example, to their sensibility to acids, until they have been
diazotized and developed, the usual developers being [beta]-naphthol,
resorcinol, phenol and phenylene-diamine.

The following Direct Colours, after being applied to cotton, may be
submitted to the above treatment, the colours produced being chiefly
blue, brown and black:--

_Blue._--Diazurine, diazo blue, diamine blue, diaminogene.

_Red._--Rosanthiene.

_Brown._--Diazo brown, diamine cutch, diamine brown, cotton brown.

_Grey and Black._--Senzo blue, diazo blue black, diazo black, diamine
black, diazo brilliant black.

(c) _Benzo Nitrol Colours._--These are certain Direct Colours, dyed on
_cotton_ in the ordinary manner, which are then developed by passing
into a diazo solution--e.g. diazotized para-nitraniline, &c. The dyed
colour here plays the part of a phenol or amine, and reacts with the
diazo compound to produce a new colour. The process is similar to the
production of the Insoluble Azo Colours, the [beta]-naphthol which is
there applied to the fibre being here replaced by a Direct Colour. The
colour of the latter is rendered much deeper by the process, and also
faster to washing and to the action of acids. The dyestuffs
recommended for application in the manner described are: Benzo nitrol
brown, toluylene brown, direct fast brown, Pluto black, direct blue
black.

_"Topping" Direct Colours._--The direct colours possess the remarkable
property of precipitating the basic colours from aqueous solution. Use
is frequently made of this property for "topping" cotton dyed with
direct colours either with a view to obtain compound shades or to
brighten the colour. Thus by dyeing cotton first yellow in chrysamine
and then dyeing it again in a cold bath of methylene blue a brilliant
shade of green results. If, on the other hand, a direct blue is topped
with methylene blue, its brilliancy may be enhanced.

MORDANT COLOURS.--The colouring matters of this class include some of
the most important dyestuffs employed, since they furnish many colours
remarkable for their fastness to light, washing and other influences.
Employed by themselves, Mordant Colours are usually of little or no
value as dyestuffs, because, with few exceptions, either they are not
attracted by the fibre, particularly in the case of cotton, or they
only yield a more or less fugitive stain. Their importance and value
as dyestuffs are due to the fact that they act like weak acids and
have the property of combining with metallic oxides to form insoluble
coloured compounds termed "lakes," which vary in colour according to
the metallic oxide or salt employed. The most stable lakes are those
in which the colouring matter is combined with two metallic oxides, a
sesquioxide and a monoxide--e.g. alumina and lime. In applying
colouring matters of this class the object of the dyer is to
precipitate and fix these coloured lakes upon and within the fibre,
for which purpose two operations are necessary, namely, _mordanting_
and _dyeing_.

The _mordanting operation_ aims at fixing upon the fibre the necessary
metallic oxide or insoluble basic salt, which is called the _mordant_,
although the term is also applied to the original metallic salt
employed. In the subsequent dyeing operation the mordanted material
is boiled with a solution of the colouring matter, during which the
metallic oxide attracts and chemically combines with the colouring
matter, producing the coloured lake _in situ_ on the fibre, which thus
becomes dyed. The mode of applying the mordants varies according to
the nature of the fibre and the metallic salt employed, the chief
mordants at present in use being salts of chromium, aluminium, tin,
copper and iron. The method of mordanting _wool_ depends upon its
property of decomposing metallic salts, and fixing upon itself an
insoluble metallic compound, when boiled in their solutions. This
decomposition is facilitated by the heating and by the dilution of the
solution, but it is chiefly due to the action of the fibre itself. The
exact nature of the substance fixed upon the fibre has not in all
cases been determined; probably it is a compound of the metallic oxide
with the wool-substance itself, which has the character of an
amido-acid. The mordant most largely employed for wool is bichromate
of potash, since, besides being simply applied, and leaving the wool
with a soft feel, it yields with the various mordant-dyestuffs a large
variety of fast colours. The wool is boiled for 1 to 1-1/2 hours in a
solution containing 2 to 3% bichromate of potash on the weight of the
wool employed. During this operation the wool at first attracts
chromic acid, which is gradually reduced to chromium chromate, so that
the mordanted fibre has finally a pale olive-yellow tint. In the
dyebath, under the influence of a portion of the dyestuff, further
complete reduction to chromic hydrate occurs before it combines with
the colouring matter. Not unfrequently certain so-called "assistants"
are employed in small amount along with the bichromate of potash--e.g.
sulphuric acid, cream of tartar, tartaric acid, lactic acid, &c. The
use of the organic acids here mentioned ensures the complete reduction
of the chromic acid on the wool to chromic hydrate already in the
mordant bath, and the pale greenish mordanted wool is better adapted
for dyeing with colours which are susceptible to oxidation--e.g.
alizarin blue. For special purposes chromium fluoride, chrome alum,
&c., are employed. Alum or aluminium sulphate (8%), along with acid
potassium tartrate (cream of tartar) (7%), is used for brighter
colours--e.g. reds, yellows, &c. The object of the tartar is to retard
the mordanting process and ensure the penetration of the wool by the
mordant, by preventing superficial precipitation through the action of
ammonia liberated from the wool; it ensures the ultimate production of
clear, bright, full colours. For still brighter colours, notably
yellow and red, stannous chloride was at one time largely employed,
now it is used less frequently; and the same may be said of copper and
ferrous sulphate, which were used for dark colours. _Silk_ may be
often mordanted in the same manner as wool, but as a rule it is
treated like cotton. The silk is steeped for several hours in cold
neutral or basic solutions of chromium chloride, alum, ferric
sulphate, &c., then rinsed in water slightly, and passed into a cold
dilute solution of silicate of soda, in order to fix the mordants on
the fibre as insoluble silicates. _Cotton_ does not, like wool and
silk, possess the property of decomposing metallic salts, hence the
methods of mordanting this fibre are more complex, and vary according
to the metallic salts and colouring matters employed, as well as the
particular effects to be obtained. One method is to impregnate the
cotton with a solution of so-called "sulphated oil" or "Turkey-red
oil"; the oil-prepared material is then dried and passed into a cold
solution of some metallic salt--e.g. aluminium acetate, basic chromium
chloride, &c. The mordant is thus fixed on the fibre as a metallic
oleate, and after a passage through water containing a little chalk or
silicate of soda to remove acidity, and a final rinsing, the cotton is
ready for dyeing. Another method of mordanting cotton is to fix the
metallic salt on the fibre as a tannate instead of an oleate. This is
effected by first steeping the cotton in a cold solution of tannic
acid or in a cold decoction of some tannin matter, e.g. sumach, in
which operation the cotton attracts a considerable amount of tannic
acid; after squeezing, the material is steeped for an hour or more in
a solution of the metallic salt, and finally washed. The mordants
employed in this case are various--e.g. basic aluminium or ferric
sulphate, basic chromium chloride, stannic chloride (cotton spirits),
&c. There are other methods of mordanting cotton besides those
mentioned, but the main object in all cases is to fix an insoluble
metallic compound on the fibre. It is interesting to note that whether
the metallic oxide is united with the substance of the fibre, as in
the case of wool and silk, or precipitated as a tannate, oleate,
silicate, &c., as in the case of cotton or silk, it still has the
power of combining with the colouring matter in the dyebath to form
the coloured "lake" or dye on the material.

The _dyeing operation_ consists in working the mordanted material in a
solution of the necessary colouring matter, the dyebath being
gradually raised to the boiling point. With many colouring matters,
e.g. with alizarin, it is necessary to add a small percentage of
calcium acetate to the dyebath, and also acetic acid if wool is being
dyed. In wool-dyeing, also, the mordanting operation may follow that
of dyeing instead of preceding it, in which case the boiling of the
wool with dyestuff is termed "stuffing," and the subsequent developing
of the colour by applying the mordant is termed "saddening," because
this method has in the past been usually carried out with iron and
copper mordants, which give dull or sad colours. The method of
"stuffing and saddening" may, however, be carried out with other
mordants, even for the production of bright colours, and it is now
frequently employed with certain alizarin dyestuffs for the production
of pale shades which require to be very even and regular in colour.
There is still another method of applying Mordant Colours in
wool-dyeing, in which the dyestuff and the mordant are applied
simultaneously from the beginning; it is known as the "single-bath
method." It is only successful, however, in the case of certain
colouring matters and mordants, to some of which reference will be
made in the following paragraphs.

_The Natural Mordant Colours._--It is interesting to note that nearly
all the natural or vegetable dyestuffs employed belong to the class of
Mordant Colours, the most important of these being included in the
following list:--_Madder, Cochineal, Peachwood, Sapanwood, Limawood,
Camwood, Barwood, Sanderswood, Old Fustic, Young Fustic, Quercitron
Bark, Persian Berries, Weld, Logwood_.

_Madder_ consists of the dried ground roots of _Rubia tinctorum_, a
plant of Indian origin. Formerly cultivated largely in France and
Holland, it was long one of the most important dyestuffs employed,
chiefly in the production of Turkey-red and in calico-printing, also
in wool-dyeing. With the different mordants it yields very distinct
colours, all fast to light and soap, namely, red with aluminium,
orange with tin, reddish brown with chromium, purple and black with
iron. Madder contains two closely allied colouring matters, namely,
alizarin and purpurin. The former, which is by far the more important,
is now prepared artificially from the coal-tar product anthracene, and
has almost entirely superseded madder.

_Cochineal_ is the dried scale-insect _Coccus cacti_, which lives on
certain of the cactus plants of Mexico and elsewhere. The rearing of
cochineal was once a large and important industry, and although still
pursued, it has seriously declined, in consequence of the discovery of
the azo scarlets derived from coal-tar. The colouring matter of
cochineal, carminic acid, is believed by chemists to be a derivative
of naphthalene, but its artificial production has not yet been
accomplished. Cochineal dyes a purple colour with chromium mordant,
crimson with aluminium, scarlet with tin, and grey or slate with iron.
Its chief employment is for the purpose of dyeing crimson, and more
especially scarlet, on wool. Crimson is dyed by mordanting the wool
with alum and tartar and dyeing in a separate bath with ground
cochineal. Scarlet on wool is obtained by the single-bath method,
namely, by dyeing the wool with a mixture of stannous chloride (or
nitrate of tin), oxalic acid, and cochineal. It is usual to add also a
small amount of the yellow dyestuff flavine in order to obtain a
yellower shade of scarlet. The cochineal colours are very fast to
light, but somewhat susceptible to the action of alkalis.

_Peachwood, Sapanwood_ and _Limawood_ are usually referred to as the
"soluble red-woods," because of the solubility in water of the
colouring principle they contain. They consist of the ground wood of
various species of _Caesalpinia_ found in Central America, the East
Indies and Peru. They all yield more or less similar colours with the
different mordants--claret-brown with chromium, red with aluminium,
bright red with tin, dark slate with iron. Owing to the fugitive
character of all the colours to light, these dyewoods are now
comparatively little employed in dyeing.

_Camwood, Barwood_ and _Sanderswood_ represent the so-called
"insoluble red-woods," their colouring principles being sparingly
soluble even in boiling water. They are obtained from certain species
of _Pterocarpus_ and _Baphia_, large trees growing in the interior of
West Africa. Their general dyeing properties are similar, a
claret-brown being obtained with chromium mordant, a brownish red with
aluminium, a brighter red with tin, and purplish brown with iron.
Their chief employment is in wool-dyeing, for the production of
various shades of brown, being best applied by the "stuffing and
saddening" method above described; but since the colours are fugitive
to light, they are now very largely replaced by alizarin. A brown on
wool is obtained by first boiling for one to two hours in a decoction
of the ground wood (50%), and then boiling in a separate bath in
solution of bichromate of potash (2%) for half an hour. These
dye-woods are also employed by the indigo-dyer, in order to give a
brownish ground colour to the wool previous to dyeing in the indigo
vat, and thus obtain a deeper, fuller blue. The colouring matters
contained in these dyewoods have not been exhaustively examined.

_Fustic_ is a yellow dyestuff, and consists of the wood of the dyer's
mulberry tree, _Morus tinctoria_, which grows in Cuba, Jamaica, &c. It
is still an important and largely used dyestuff, being cheap, and the
colours obtained from it being satisfactorily fast to light and other
influences. With chromium mordant it yields an olive-yellow or
"old-gold" shade; with aluminium, yellow; with tin, a brighter yellow;
with iron, an olive-green. It is chiefly employed in wooldyeing along
with other dyestuffs, and furnishes the yellow in compound shades. Two
colouring principles exist in Old Fustic, namely, morin and maclurin,
the former being the most important, and generally regarded as the
true colouring matter.

_Quercitron Bark_ consists of the inner bark of an oak-tree, _Quercus
tinctoria_, which grows in the North American States. It dyes somewhat
like Old Fustic, but gives with aluminium and tin mordants brighter
yellows, for which colours it is chiefly used. The colouring principle
of Quercitron Bark is called quercitrin, which by the action of
boiling mineral acid solutions is decomposed, with the production of
the true colouring matter termed quercetin.

So-called _Flavine_ is a commercial preparation of Quercitron Bark
consisting of quercitrin or of quercetin; it is much used by
wool-dyers for the production of bright yellow and orange colours.
Wool is dyed in single bath by boiling with a mixture of Flavine (8%),
stannous chloride (4%) and oxalic acid (2%). Flavine is used in small
quantity along with cochineal for dyeing scarlet on wool.

_Persian Berries_ are the dried unripe fruit of various species of
_Rhamnus_ growing in the Levant. The general dyeing properties are
similar to those of Quercitron Bark, the orange colour given with tin
mordant being particularly brilliant. The high price of this dyestuff
causes its employment to be somewhat limited. The colouring matter of
Persian Berries is called xanthorhamnin, which by the action of
fermentation and acids yields the true dyestuff rhamnetin.

_Weld_ is the dried plant _Reseda luteola_, a species of wild
mignonette, formerly largely cultivated in Europe. Its dyeing
properties resemble those of Quercitron Bark, but the yellows with
aluminium and tin mordants are much brighter and purer, and also
faster to light. It is still used to a limited extent for dyeing a
bright yellow on woollen cloth and braid for the decoration of
military uniforms. Quite recently the colouring matter of Weld,
namely, luteolin, has been prepared artificially, but the process is
too expensive to be of practical use.

_Logwood_ is the heart-wood of _Haematoxylon campechianum_, a tree
growing in Central America. It is the most important natural dyewood
at present employed, being largely used for dyeing dark blues and
black on silk, wool and cotton. With chromium and aluminium mordants
logwood dyes a dark blue, and even black; with tin, a dark purple; and
with iron, black. The colours are only moderately fast to light. On
wool the mordant is bichromate of potash; on cotton and silk an iron
mordant is employed. Before use by the dyer the logwood is ground and
aged or oxidized, by allowing moistened heaps of the ground wood to
ferment slightly, and by frequently turning it over to expose it
freely to the air. By this means the colouring principle haematoxylin
which logwood contains is changed into the true colouring matter
haematein. The constitution of this colouring matter has been recently
discovered; it is very closely allied to the brazilin of peachwood,
sapanwood and limawood, and is also a member of the [gamma]-pyrone
group of colouring matters.

The importance of the above-mentioned natural dyestuffs is gradually
diminishing in favour of mordant dyestuffs and others derived from
coal-tar. Fustic and logwood are perhaps the most largely used, and
may continue to be employed for many years, no satisfactory artificial
substitutes having hitherto come into the market.

The _Artificial Mordant_ Colours are well represented by alizarin, the
colouring matter of the madder root, which was the first natural
dyestuff prepared artificially from the coal-tar product anthracene
(1868). For this reason many of these colours are frequently referred
to as the Alizarin Colours. At the present time, however, there are
numerous Mordant Colours which are prepared from other initial
materials than anthracene; they are not chemically related to
alizarin, and for these the term Alizarin Colours is therefore
inappropriate. The property, which Mordant Colours possess in common,
of combining with metals and producing lakes, which readily adhere to
the fibre, depends upon their chemical constitution, more particularly
upon the general and relative position in the molecule of certain side
atomic groups. In alizarin there are, for example, two characteristic
hydroxyl groups (OH) occupying a special (ortho) position in the
molecule, i.e. they are next to each other, and also next to one of
the socalled ketone groups (C:O). In other Mordant Colours there are
carboxyl (COOH) as well as hydroxyl groups, which are all-important in
this respect. In addition to this, the general dyeing property is
influenced by the constitution of the molecule itself, and by the
presence of other side-groups, e.g. NH2, HSO3, &c., which modify the
colour as to solubility or hue. Hence it is that the members of this
group, while possessing the mordant-dyeing property in common, differ
materially in other points. Some, like alizarin, are not in themselves
to be regarded as colouring matters, but rather as colouring
principles, because they only yield useful dyes in combination with
metallic oxides. According to their constitution, these may yield one
or many colours with the various metallic oxides employed, and they
are used for cotton as well as for wool and silk. Other Mordant
Colours, e.g. many of the Direct Colours and others, are capable of
dyeing either the vegetable or animal fibres without the aid of a
mordant; they are fully developed colouring matters in themselves, and
possess the mordantdyeing property as an additional feature, in
consequence of the details of their chemical constitution, to which
reference has been made in the foregoing paragraphs. As a rule these
yield, at most, various shades of one colour with the different
oxides, and are only suitable for the animal fibres, particularly
wool.

In the following list, the most important artificial Mordant Colours
are arranged according to the colour they give in conjunction with the
aluminium mordant, unless otherwise indicated. Some of those named
here dye the animal fibres, even without mordants; some are Direct
Colours possessing mordant-dyeing properties, others are sulphonic
acid derivatives of Alizarin Colours, suitable for wool but not for
cotton.

_Red._--Alizarin, anthrapurpurin, flavopurpurin, purpurin, alizarin
Bordeaux, alizarin garnet R, alizarin maroon, alizarin S, cloth red,
diamine fast red, anthracene red, chrome red, chrome Bordeaux,
salicine red, erio chrome red, emin red, milling red.

_Orange and Yellow._--Alizarin orange, alizarin orange G, alizarin
yellow paste, alizarin yellow A, alizarin yellow C, anthracene yellow,
galloflavin, alizarin yellow GG, alizarin yellow R, diamond flavin G,
chrome yellow D, Crumpsall yellow, fast yellow, diamond yellow, benzo
orange R, cloth orange, carbazol yellow, chrysamine, milling orange.

_Green._--Coerulein, coerulein S, alizarin green S, fast green (Fe),
naphthol green (Fe), Dioxin (Fe), Gambine (Fe), azo green, gallanil
green, alizarin green G and B, acid alizarin green, alizarin cyanine
green, alizarin viridine, diamond green, chrome green, Domingo green.

_Blue._--Alizarin blue, alizarin blue S, alizarin cyanine, anthracene
blue, brilliant alizarin blue, alizarin indigo blue S, gallanilic
indigo, acid alizarin blue, brilliant alizarin cyanine, alizarin
grisole, alizarin sky blue, alizarin saphirole, gallanilide blue,
delphine blue, gallamine blue, celestine blue, chrome blue, gallazine
A, phenocyanine, coreine.

_Purple and Violet._--Gallein, alizarin heliotrope, anthraquinone
violet, chrome prime, gallocyanine, chrome violet, anthracene chrome
violet.

_Brown._--Anthracene brown, chromogen, cloth brown, diamond brown,
alizarin brown, fast brown, alizarin acid brown, chrome brown,
palatine chrome brown, erio chrome brown.

_Black._--Alizarin black, diamond black, alizarin blue black, alizarin
cyanine black, alizarin fast grey, chromotrope, chrome black, erio
chrome black, anthracite black, acid alizarin black, anthracene chrome
black.

A brief description of the application of a few of the more important
of the above colouring matters will suffice.

_Alizarin_, _Anthrapurpurin_ and _Flavopurpurin_ give somewhat similar
shades with the different mordants, namely, brown with chromium, red
with aluminium, orange with tin, and purple with iron.